Flask

See every request your Flask app handles (the route, how long it took, the response status, and any errors) as a trace (the full journey of one request, made of nested spans, where each span is one unit of work with a name, a start, and a duration) in Logfire.

What you’ll capture

Each request as a span, with its HTTP status and duration
The matched route and method
Any errors raised while handling the request

Before you start

You’ll need a Logfire project. Open Add data in your project (top navigation) and follow the setup for your language: it signs your machine in with logfire auth (a browser sign-in, no token to copy) and, for production or other languages, creates a write token (the credential your app uses to send data). New to Logfire? Start with Getting Started.

Installation

Install logfire with the flask extra:

Terminal

pip install 'logfire[flask]'

Terminal

uv add 'logfire[flask]'

Usage

Add two lines to your app: logfire.configure() to connect to your project, and logfire.instrument_flask() to record every request.

main.py

from flask import Flask

import logfire

logfire.configure()

app = Flask(__name__)
logfire.instrument_flask(app)


@app.route('/')
def hello():
    return 'Hello!'


if __name__ == '__main__':
    app.run(debug=True)

Run it with python main.py.

Verify it worked

With the app running, open http://localhost:5000/ in your browser.

Then open your project in the Logfire web app and go to the Live view. Within a few seconds you should see a span for the request. Click it to see its duration, the matched route, and the response status.

Troubleshooting

Not seeing your requests in Logfire? Check these first:

logfire.configure() runs before logfire.instrument_flask(). Configure the connection first, then instrument the app.
You call instrument_flask(app) exactly once, on the same app object you serve.
Your write token is set. In local development, run logfire projects use <your-project>; in production, set the LOGFIRE_TOKEN environment variable. See Getting Started.
You actually sent a request. Spans appear only after a route is hit; reload the URL above.

Advanced

Passing options to the OpenTelemetry instrumentor

logfire.instrument_flask() accepts additional keyword arguments and passes them to the OpenTelemetry FlaskInstrumentor().instrument_app() method. See their documentation for the full list.

Running under Gunicorn

If you run your Flask application with Gunicorn, you can also configure Logfire in Gunicorn.

Reference

API reference: logfire.instrument_flask()
Underlying OpenTelemetry package: Flask instrumentation